Beginner's Guides

I am 30 with a background of business Administration degree and a passion for writing (writing and editing). I've heard about copywriting a lot in past but knew nothing about it. Just recently I came upon a post which gave me a little insight into the field and I am kind of intrigued. I'm at a point where I'm have to choose a career field. Is copywriting worth pursuing? I'll be doing it as a freelancer. If yes then how and where should I start?.

Is there a guide I can read through? Exercises I'll need to practice with? A mentor I could follow?